The seasonal and longer-term dynamics of fuel accumulation affect fire seasonality and the occurrence of extreme wildfires. Failure to account for their influence may
help to explain why state-of-the-art fire models do not simulate the length and timing of the fire season or interannual variability in burnt area well. We investigated the impact of accounting for different timescales of fuel production and accumulation on burnt area using a suite of random forest regression models that included the immediate
impact of climate, vegetation, and human influences in a
given month and tested the impact of various combinations
of antecedent conditions in four productivity-related vegetation indices and in antecedent moisture conditions. Analyses were conducted for the period from 2010 to 2015 inclusive. Inclusion of antecedent vegetation conditions representing fuel build-up led to an improvement of the global,
climatological out-of-sample R
2
from 0.579 to 0.701, but the
inclusion of antecedent vegetation conditions on timescales
≥ 1 year had no impact on simulated burnt area. Current
moisture levels were the dominant influence on fuel drying. Additionally, antecedent moisture levels were important
for fuel build-up. The models also enabled the visualisation
of interactions between variables, such as the importance
of antecedent productivity coupled with instantaneous drying. The length of the period which needs to be considered
varies across biomes; fuel-limited regions are sensitive to antecedent conditions that determine fuel build-up over longer
time periods (∼ 4 months), while moisture-limited regions
are more sensitive to current conditions that regulate fuel drying.